Question

A light of wavelength $310\, nm$ is used in a photoelectric experiment. The metal electrode of work function of $2.5\,eV$ is used in the experiment. The stopping potential for the photoelectrons will be(Assume $hc =1240\, eV - nm$)

• A. 1.0 V
• B. 1.5 V
• C. 2.0 V
• D. 2.5 V

Answer 1

Answer: (B)

Work-function of metal surface, $\varphi_{0}=25\, eV$
Wavelength, $\lambda=310\, nm$
$\Rightarrow h c=1240\, eV - nm$
According to Einstein's photoelectric equation,
$e V_{0}=\frac{h c}{\lambda}-\varphi_{0}$
$\Rightarrow e V_{0}=\frac{1240\, eV -n m}{310\, nm }-2.5\, eV$
$\Rightarrow V_{0}=\frac{1240}{310}-25=4-25=1.5\, V$